Vacuum pump

ABSTRACT

A rotating vane vacuum pump has a secondary inlet ( 4 ) which permits additional suction after the primary inlet ( 3 ) has closed.

The present invention relates to a vacuum pump and in particular, thoughnot exclusively, to a vacuum pump for use in conjunction with anautomotive braking system.

Sliding vane vacuum pumps are known to suffer from reduced efficiencywhen operating at low speed, because of internal leakage within thepump. At high operating speeds the time interval between opening andclosing of the pump inlet is reduced, and leakage can be containedwithin acceptable limited. Leakage at relatively low speeds can bereduced by the use of special materials for the vane tips, and reducedclearance between the vane tips and the pump casing. However suchmeasures tend to increase the cost of the pump significantly. What isrequired is a pump which can operate more efficiently at low speeds.

According to the present invention there is provided a vacuum pumpcomprising a casing defining a chamber, the chamber having a firstinlet, an outlet, a rotor rotatable in the chamber and a vane slidablysupported by said rotor, the vane being rotatable so as to draw fluidfrom the first inlet into the chamber and subsequently expel said fluidthrough the outlet, wherein the chamber is provided with a second inletadapted to permit fluid to be drawn into the chamber after closure ofthe first inlet and to be exhausted through the outlet.

Thus at no time are both inlets connected to the pump chamber at thesame time.

The second inlet permits some work to be performed by the pump during agreater portion of the rotary cycle. It will be appreciated that boththe inlets are fed from a common chamber and exhaust through a commonoutlet of the pump. The pump may be provided with more than one vane.

The inlets are positioned such that fluid, typically air, is drawnsequentially therethrough into the chamber as the vane is rotated. Theinlets inlet are preferably provided with non return means so as toprevent air being returned to the reservoir as it is expelled throughthe outlet. The inlets may be connected to a common reservoir.Alternatively the first and second inlets may be connected to differentreservoirs.

The inlets may be connected to the reservoir by a common feed line. Insuch an embodiment there may be provided a single feed line extendingfrom the reservoir to the first inlet, the casing being drilled so as toallow fluid communication from said feed line to the second inlet.Alternatively the inlets may have separate connections to the reservoir.

The vane of the pump may be provided with tips which are caused bycentripetal forces to contact the pump chamber. In such an embodimenteach tip may comprise an insert retained to the vane. The insert may beprovided with a projection which is received with a sliding fit in acorresponding recess of the vane. The projections and recesses of thevane and tip may be reversed.

A vacuum pump in accordance with the invention will now be described byway of example with reference to the accompanying drawings in which:

FIG. 1 is a diagrammatic cross section of a vacuum pump according to thepresent invention;

FIG. 2 is a diagrammatic cross section of an alternative embodiment of avacuum pump according to the present invention; and

FIG. 3 is a diagrammatic representation of a vane end and tip.

Referring firstly to FIG. 1, there is shown a vacuum pump, generallydesignated 1, having a chamber 2 of constant depth and having agenerated shape accordingly to the circular motion of a vane 10, to bedescribed. The body has a main inlet 3 provided with a non-return valve14, a secondary inlet 4 provided with a non return valve 5, and anoutlet 6. The inlets 3,4 may be connected to separate consumers, such asseparate reservoirs 7 a, 7 b, or a common reservoir 7. Broken line 15 isemployed for the sake of simplicity to represent the common 7 orseparate 7 a, 7 b reservoirs. The pump 1 is operable to partiallyevacuate the or each reservoir 7,7 a, 7 b. The outlet 6 is vented in anysuitable manner, for example to atmosphere, or in the case of an I.C.engine to the crank case.

Within the pump body there is provided an off-centre rotatable hub 8having a slot 9 within which a blade or vane 10 is free to slide. Therespective ends of the vane 10 make contact with the internal surface ofthe chamber 2 to provide a seal therebetween as the vane 10 is rotatedby the hub 8. The internal shape of the chamber 2 corresponds to thedesired motion of the vane 10, and is arranged to be in close contactwith the tips of the vane 10 at all times. The tips of the vane 10 mayfloat in order to provide improved sealing due to centripetal forces aswill be described in greater detail below.

As the vane 10 is rotated in an anticlockwise direction indicated inFIG. 1 it sweeps across the position where the main inlet 3 connects tothe chamber 2. This position is indicated as position A in the figure.As the vane 10 moves anticlockwise, area B, which can be considered tobe behind the vane 10 in the direction of rotation, expands. Theincrease in size of area B lowers the pressure within the chamber 2 thuscausing air to flow from the reservoir 7 or first reservoir 7 b throughthe main inlet and into the chamber 2. Continued rotation of the vane 10draws further air into the chamber 2.

Eventually the vane 10 is rotated to a position where the opposite endportion thereof, sweeps across the main inlet 3/chamber connectionthereby isolating the hitherto expanding area B from the main inlet 3.The pressure within the now isolated area B is still less than that ofthe reservoir 7. Continued rotation of the vane 10 causes it to sweepacross the position where the secondary inlet 4 connects to the chamber2 thus re-establishing fluid communication between the reservoir 7 andthe chamber 2 or, alternatively, establishing fluid communicationbetween the second reservoir 7 a and the chamber 2. Due to the factthat, as noted above, the pressure within the pump body 2 is less thanthe reservoir 7,7 a, additional air is drawn from the reservoir 7,7 athrough the secondary inlet 4 and into the chamber 2.

As the vane 10 continues to rotate it sweeps across the position wherethe outlet 6 meets the chamber 2. Thereafter area B starts to reduce andthereby pushing the air drawn into the chamber 2 from the reservoir 7 orreservoirs 7 a, 7 b to atmosphere. The non return valves 5, 14 preventthe air from flowing back to the reservoir 7 or reservoirs 7 a, 7 b viathe inlets 3,4.

Referring now to FIG. 2 there is shown a further embodiment of thepresent invention. Features common to the embodiment described withreference to FIG. 1 are identified with like reference numerals. Thepump 1 of FIG. 2 differs from that of FIG. 1 in that the pump inlets 3,4are connected to the reservoir by a common feed line 12. In thisembodiment the secondary inlet 4 is connected to the feed line 1-2 viaan internal cross drilling 11 of the pump casing. In an alternativeembodiment (not shown) the secondary inlet may comprise a separateconduit extending between the feed line and a secondary inlet port onthe pump. As before both inlets 3,4 are provided with non return valves16, 17 to prevent air drawn into the chamber from being returned to thereservoir 7.

Referring now to FIG. 3 there is shown an embodiment of a vane tip 20.The tip 20 is mounted to an end of a vane 10. In use, the tip 20 runsalong the curved wall 22 of a pump chamber 2 to provide a seal and toprevent fluid, typically air, from leaking across the end of the vane10. The tip 20 is provided with a projection 24 which is received with asliding fit in a correspondingly shaped recess 26 of the vane 10. Thetip 20 is provided with a curved end 28 shaped to fit in a requiredmanner to the wall 22. In use, the sliding nature of the fit between thetip 20 and the vane 10 ensures that the tip 20 is urged into contactwith the wall 22 by the centripetal forces resulting from rotation ofthe vane 10.

The present invention increases the efficiency of the pump, especiallywhen operating at elevated rotational speeds, by maximising the amountof air drawn from the reservoir per rotation of the hub and vane.

1. A vacuum pump comprising a casing defining a chamber, the chamberhaving a first inlet, an outlet, a rotor rotatable in the chamber and asingle vane that is slidably supported by a slot extending fully acrosssaid rotor, the vane being rotatable so as to draw fluid from the firstinlet into the chamber and subsequently expel said fluid through theoutlet, wherein the chamber is provided with a second inlet adapted topermit fluid to be drawn into the chamber after closure of the firstinlet by rotation of the vane, and before expelling said fluid in thechamber through the outlet.
 2. A vacuum pump as claimed in claim 1wherein the first and second inlets are provided with non return meansto prevent outflow of fluid therethrough.
 3. A vacuum pump comprising acasing defining a chamber, the chamber having a first inlet, an outlet,a rotor rotatable in the chamber and a vane slidably supported by saidrotor, the vane being rotatable so as to draw fluid from the first inletinto the chamber and subsequently expel said fluid through the outlet,wherein the chamber is provided with a second inlet adapted to permitfluid to be drawn into the chamber after closure of the first inlet andto be exhausted through the outlet, wherein the inlets are branched froma common feed line.
 4. A vacuum pump as claimed in claim 3 and having aninternal duct connecting said first and second inlets.
 5. A vacuum pumpas claimed in claim 1 or claim 2, wherein the first and second inletsare separate.
 6. A vacuum pump as claimed in claim 1, wherein said vaneis provided with a separate vane tips, said vane tips being adapted tobe urged into contact with the wall of said chamber by rotation of thevane.
 7. A vacuum pump as claimed in claim 6, wherein said vane tips areprovided with a projection which is received with a sliding fit in acorrespondingly shaped recess of the vane, so as to permit relativeradial movement thereof.
 8. A vacuum pump as claimed in claim 1, whereinsaid vane is provided with a projection which is received with a slidingfit in a correspondingly shaped recess of the vane tip, so as to permitrelative radial movement thereof.
 9. A vacuum pump as claimed in claim3, wherein said vane is provided with a separate vane tips, said vanetips being adapted to be urged into contact with the wall of saidchamber by rotation of the vane.
 10. A vacuum pump as claimed in claim9, wherein said vane tips are provided with a projection which isreceived with a sliding fit in a correspondingly shaped recess of thevane, so as to permit relative radial movement thereof.
 11. A vacuumpump as claimed in claim 3, wherein said vane is provided with aprojection which is received with a sliding fit in a correspondinglyshaped recess of the vane tip, so as to permit relative radial movementthereof.
 12. A vacuum pump as claimed in claim 3, and having a pluralityof vanes.
 13. A vacuum pump as claimed in claim 3, wherein the first andsecond inlets are provided with non return means to prevent outflow offluid therethrough.
 14. A vacuum pump as claimed in claim 3, wherein thefirst and second inlets are separate.
 15. A vacuum pump as claimed inclaim 1, and having an internal duct connecting said first and secondinlets.